We present an impedance engineered Josephson parametric amplifier capable of providing bandwidth beyond the traditional gain-bandwidth product. We achieve this by introducing a positive linear slope in the imaginary component of the input impedance seen by the Josephson oscillator using a λ/2 transformer. Our theoretical model predicts an extremely flat gain profile with a bandwidth enhancement proportional to the square root of amplitude gain. We experimentally demonstrate a nearly flat 20 dB gain over a 640 MHz band, along with a mean 1-dB compression point of -110 dBm and near quantum-limited noise. The results are in good agreement with our theoretical model.Josephson parametric amplifiers (JPAs) have become a crucial component of superconducting qubit 1 measurement circuitry, enabling recent studies of quantum jumps 2 , generation and detection of squeezed microwave field 3 , quantum feedback 4,5 , real-time tracking of qubit state evolution 6-8 and quantum error detection 9,10 . Although JPAs based on Josephson junctions embedded in a resonator 11-13 regularly achieve 20 dB power gain and quantum-limited noise, typical bandwidth is restricted to 10-50 MHz 11,14 , making them suitable for single qubit measurements only. The rapid progress towards multi-qubit architectures 9 for fault-tolerant quantum computing 15,16 demands an amplifier with much larger bandwidth to enable simultaneous readout of multiple qubits with minimal resources.There have been several attempts in this direction in recent years. One such attempt used a broadband impedance transformer 17 to lower the quality factor of a lumped-element Josephson oscillator which is the main component of a parametric amplifier. While the observed large bandwidth was qualitatively explained by a model consisting of a negative resistance 18 coupled to a frequency dependent impedance, no clear prescription on the design principle was provided. A different approach using Josephson non-linear transmission lines 19,20 was recently demonstrated 21,22 with nearly 4 GHz of bandwidth. However, this design requires fabrication of about 2000 nearly identical blocks of oscillator stages, demanding fairly sophisticated fabrication facilities. Multimode systems utilizing dissipative interactions have also been suggested theoretically as a route for enhancing bandwidth 23 , but have not been realized experimentally. In this Letter, we present a simple technique for enhancing the bandwidth of a JPA and beating the standard gain-bandwidth limit. It involves engineering the imaginary part of the environmental impedance: in particular, we introduce a positive linear slope in the imaginary component of the impedance shunting the JPA, while keeping the real part unchanged at the pump frequency. Our design uses a combination of a λ/4 and a λ/2 impedance transformers which are significantly easier to fabricate than a broadband impedance transformer 17 . Our theoretical model explains why the imaginary part of the impedance plays a crucial role in determining the amplifier bandw...

It has recently been demonstrated that black hole dynamics at large D is dual to the motion of a probe membrane propagating in the background of a spacetime that solves Einstein's equations. The equation of motion of this membrane is determined by the membrane stress tensor. In this paper we 'improve' the membrane stress tensor derived in earlier work to ensure that it defines consistent probe membrane dynamics even at finite D while reducing to previous results at large D. Our improved stress tensor is the sum of a Brown York term and a fluid energy momentum tensor. The fluid has an unusual equation of state; its pressure is nontrivial but its energy density vanishes. We demonstrate that all stationary solutions of our membrane equations are produced by the extremization of an action functional of the membrane shape. Our action is an offshell generalization of the membrane's thermodynamical partition function. We demonstrate that the thermodynamics of static spherical membranes in flat space and global AdS space exactly reproduces the thermodynamics of the dual Schwarzschild black holes even at finite D. We study the long wavelength dynamics of membranes in AdS space, and demonstrate that the boundary 'shadow' of this membrane dynamics is boundary hydrodynamics with with a definite constitutive relation. We determine the explicit form of shadow dual boundary stress tensor upto second order in derivatives of the boundary temperature and velocity, and verify that this stress tensor agrees exactly with the fluid gravity stress tensor to first order in derivatives, but deviates from the later at second order and finite D. 4 The constant λ in (1.4) is proportional to (minus of) the usual cosmological constant. We have chosen the normalization of λ to ensure that AdS D with radius 1 √ λ is a solution the equations (1.4) when λ is positive, while de Sitter space with radius 1 √ −λ solves (1.4) when λ is negative. Upon setting λ = 0 (1.4) reduces to the usual (flat space) vacuum Einstein equations.

We study four-point functions of scalars, conserved currents, and stress tensors in a conformal field theory, generated by a local contact term in the bulk dual description, in two different causal configurations. The first of these is the standard Regge configuration in which the chaos bound applies. The second is the ‘causally scattering configuration’ in which the correlator develops a bulk point singularity. We find an expression for the coefficient of the bulk point singularity in terms of the bulk S matrix of the bulk dual metric, gauge fields and scalars, and use it to determine the Regge scaling of the correlator on the causally scattering sheet in terms of the Regge growth of this S matrix. We then demonstrate that the Regge scaling on this sheet is governed by the same power as in the standard Regge configuration, and so is constrained by the chaos bound, which turns out to be violated unless the bulk flat space S matrix grows no faster than s2 in the Regge limit. It follows that in the context of the AdS/CFT correspondence, the chaos bound applied to the boundary field theory implies that the S matrices of the dual bulk scalars, gauge fields, and gravitons obey the Classical Regge Growth (CRG) conjecture.

In this paper, we have found a class of dynamical charged 'black-hole' solutions to Einstein-Maxwell system with a non-zero cosmological constant in a large number of spacetime dimensions. We have solved up to the first sub-leading order using large D scheme where the inverse of the number of dimensions serves as the perturbation parameter. The system is dual to a dynamical membrane with a charge and a velocity field, living on it. The dual membrane has to be embedded in a background geometry that itself, satisfies the pure gravity equation in presence of a cosmological constant. Pure AdS / dS are particular examples of such background. We have also obtained the membrane equations governing the dynamics of charged membrane. The consistency of our membrane equations is checked by calculating the quasi-normal modes with different Einstein-Maxwell System in AdS/dS. arXiv:1806.08515v3 [hep-th] 13 Dec 2018Firstly, they generate a new class of dynamical black hole solutions of Einstein equations which are very difficult to solve otherwise (even numerically). Secondly, through these constructions, we could see a duality between the dynamical horizons of the black hole/brane metric and a co-dimension one dynamical membrane, embedded in the asymptotic background geometry. This membrane-gravity duality allows us to analyse the complicated dynamics of the black holes from a different angle, which might turn out to be useful in future for some realistic calculation.In this paper, our goal is to extend the 'background covariant' technique of [35] to Einstein-Maxwell system in presence of cosmological constant. For this case, the dual system would be a codimension-one dynamical charged membrane, embedded in the asymptotic dS / AdS metric. The motivation for our work is two-fold. The first is, of course, to see how the whole technique of background-covariantization works for Einstein-Maxwell system, which, in terms of complexity, is just at the next level, compared to the pure gravity system. Indeed we have noticed that unlike the uncharged case, only naive covariantization of the flat spaceequations of the charged membrane (as derived in [9]) will not give the correct duality and we need to add a term proportional to the background curvature even at the first subleading order in O 1 D expansion. This is indeed one of the interesting observations in our paper. The second piece of motivation is as follows. We know that in asymptotically AdS geometry there exist another set of perturbative solutions to Einstein-Maxwell system. These are black holes/branes constructed in a derivative expansion and are dual to dynamical charged fluid living at the boundary of AdS. Recent works can be found in [18,34,38]. At this point, it is natural to ask whether there exists any overlap regime for these two types of perturbations, and if so, whether the two metrics agree. In the best possible scenario, the outcome of this comparison could be a duality between the dynamics of a charged fluid and charged membrane in a large number of dimensions, wh...

We present the "trimon", a multi-mode superconducting circuit implementing three qubits with all-to-all longitudinal coupling. This always-on interaction enables simple implementation of generalized controlled-NOT gates which form a universal set. Further, two of the three qubits are protected against Purcell decay while retaining measurability. We demonstrate high-fidelity state swapping operations between two qubits and characterize the coupling of all three qubits to a neighbouring transmon qubit. Our results offer a new paradigm for multi-qubit architecture with applications in quantum error correction, quantum simulations and quantum annealing.Controlling and manipulating the interactions between multiple qubits is at the heart of quantum information processing, and the superconducting circuit architecture 1 has emerged as a leading candidate. Previous demonstrations of multi-qubit devices 2-8 have used transmon qubits 9 along with separate coupling elements to implement transverse inter-qubit coupling. Typically, this transverse coupling is weak and restricted to nearest neighbours which limits the kind of multi-qubit operations that can be performed. Recently, longitudinal inter-qubit coupling has been proposed as an alternative for building a universal multi-qubit architecture [10][11][12] and for quantum annealing architectures with all-to-all coupling 13 . While the transmon design uses a single anharmonic oscillator mode to implement a qubit, this idea can be extended to a circuit that can support several oscillator modes to implement a multi-qubit system with strong longitudinal coupling 14,15 . However, previous experiments 16,17 have not demonstrated multi-qubit operations and their coherence times have not matched that of typical transmon qubits.In this Letter, we present a new quantum device, the "Trimon", implementing a three-qubit system that arises from a single superconducting circuit. Our device ( Fig. 1(a)) is based on the Josephson ring modulator (JRM) consisting of four nominally identical Josephson junctions in a superconducting loop to implement three orthogonal electrical modes 18 . This three-mode structure has been previously exploited to couple different harmonic oscillators for parametric amplification 19 , while more recently, it has been proposed as a coupling element between two qubits 13 . Here, we capacitively shunt the JRM by connecting superconducting pads to each node (Fig. 1(b)) to create three coupled anharmonic oscillator modes: two dipolar and one quadrupolar ( Fig. 1(c)). Each mode has properties similar to 3D-transmon qubits 20 with the resonant frequency and anharmonicity controllable by design. The longitudinal inter-qubit coupling 13 of the cross-Kerr type originates due to the sharing of the four junctions amongst all three modes. One of the two dipolar modes couples directly to the host 3D electromagnetic cavity ( Fig. 1(c)); we call this the "A" qubit. The other dipolar mode (qubit B) and the quadrupolar mode (qubit C) ideally stay uncoupled from the cavity an...